1. Field of the Invention
The invention relates to a high-voltage switch, in particular for a microwave generator, which includes a high-voltage source and a plurality of spark gaps each having two electrodes. A fuse is connected in series with each spark gap, and these series circuits are connected to each other in a parallel circuit.
High-voltage switches of the type mentioned initially are used in many fields of application, in which high voltages have to be switched, across which a capacitor structure, which is charged via the applied high voltage, can be discharged. When the charging voltage reaches the breakdown voltage of the spark gap, whose withstand voltage is in the end dependent on the dielectric that is used, then this results in the striking of the arc, the spark gap becomes conductive, and the capacitively stored energy can be discharged.
By way of example, a microwave generator is one application example in which a high pulse energy high-voltage pulse is intended to be switched. The operation of a generator such as this is based on a high-voltage source, for example a capacitor bank which is charged in parallel on the basis of the Marx surge-voltage circuit principle and is then connected in series, is discharged across the spark gap of the high-voltage switch. A pulse discharge process such as this leads to a rapidly rising and highly oscillating current flow, and thus to a correspondingly broadband radiated emission of a microwave spectrum with such a high energy density that radio traffic can be at least adversely affected in the vicinity of a microwave generator such as this, and, in particular, the input side of an electronic circuit can be interfered with or even destroyed.
A high-voltage generator powered by explosive can also be used as a high-voltage source and, in comparison with conventional high-voltage generators, can provide a single high-voltage pulse with an extremely high pulse energy. The output pulse which can be produced by an explosive-powered generator such as this is able, for example, to charge a capacitance of 2 nF to a voltage of 1 MW, which corresponds to a pulse energy of 1 kJ.
2. Discussion of the Prior Art
Capacitor structures, such as those which are used in the microwave generators of the type described are, however, not able to temporarily store such high energies and to emit them as a high-power microwave pulse. It would admittedly be possible to increase the capacitor capacitance, and thus the capacitance of the transmitting antenna. However, this leads to a change in the resonance behavior of the structure, the resonant frequency falls, in which case the antennas required must at the same time be designed to be very large for effective radiated emission, and this is undesirable. A further limiting factor is the withstand voltage of the spark gap of the high-voltage switch, which shorts the pulse-forming line of the resonator antenna in the microwave generator. Either spark gaps with a gaseous or a liquid dielectric are used in this case, with the triggering electrodes being positioned at a distance of about 2 mm from one another, in order to achieve switching-on losses that are as low as possible. The withstand voltage could admittedly be increased by increasing the separation, but this would result in an increase in the losses, without the effective radiated microwave field being increased. Spark gaps with a solid dielectric are known as an alternative to the use of liquid or gaseous dielectrics. These have a considerably higher breakdown voltage than dielectric liquids or high-pressure gases, that is to say the withstand voltage can be increased considerably, up to 1.5-2 MV. When they break down, solid spark gaps such as these have a very high current rate of rise, and thus low switching-on losses associated with this. However, they have the disadvantage that the solid dielectric is destroyed when it breaks down, and self-healing is impossible—in contrast to the situation with liquid or gaseous dielectrics. In consequence, solid dielectric switches such as these can be used only for a single discharge, and thus to emit only one pulse. Although solid dielectric switches such as these allow the withstand voltage of the spark gap to be increased into the MV range, it is nevertheless impossible, for the reasons described above, to effectively use the extremely high pulse energy which is provided, for example, by an explosive-powered high-voltage generator.
DE 103 13 045 B3 discloses a switching apparatus which is intended to trip in response to an overvoltage. This known switching apparatus has spark gaps which each have two electrodes, which are connected in parallel and are provided in each parallel part with a fuse connected in series with the spark gap. The respective fuse is irreversibly destroyed when a breakdown occurs across the spark gap. The respective spark gap may have a gaseous dielectric.
U.S. Pat. No. 5,489,818 describes a compact high-energy microwave generator. This known microwave generator has a cavity resonator which has two opposite electrodes which are shorted very quickly in order to produce a high-energy microwave pulse. The cavity resonator contains a liquid dielectric.
U.S. Pat. No. 3,398,322 discloses a high-voltage switch which has a gap in which a gaseous dielectric is located, such as air, nitrogen or sulfur hexafluoride, or a liquid dielectric, such as a dielectric oil, or a solid dielectric, such as polyethylene or Mylar.
DE 35 87 679 T2 discloses a fuse with a fuse element which extends between two connections in a housing and has at least two parallel-connected conductors, and at least one core composed of insulation material. In this case, one conductor may be a glass fiber, and one conductor may be a copper wire. By way of example, the copper wire may have a diameter of 25 μm or 50 μm. The diameter of the respective copper wire and the combination of copper wires to the glass fibers depends on the rated current of the fuse and on the desired response behavior of the fuse.